The present invention relates to a press brake for bending a workpiece between an upper mold set on a ram and a lower mold set on a bed, and comprises an adjusting unit for adjusting the distance between the upper and lower molds on a workpiece being bent.
In the case of bending a workpiece via a press brake, since a ram and a bed are deflected because of pressure generated in the course of the bending operation, strictly speaking, an angle for bending the workpiece can not be kept constant throughout the whole bending length. In order to correct the error of the bending angle, adjustments are necessary to keep the distance between the upper and lower molds along the length thereof constant during the bending process. To deal with this problem, conventional press brakes are provided with an adjusting unit for adjusting between molds, based on a variety of principles.
FIG. 12 exemplifies structure of such a conventional press brake incorporating an adjusting unit 100.
The reference numeral 101 shown in FIG. 12 designates an upper mold secured to a ram 104 via a holder 103, whereas the reference numeral 102 designates a lower mold held on a table 105. The adjusting unit 100 utilizes the principle of a wedge by way of combining a stationary wedge 111 with a movable wedge 112 to make up a wedging unit 110, which is installed between a bed 106 the table 105.
The movable wedge 112 is interlinked with a reciprocating unit 120 driven by a motor 121. By causing the motor 121 to rotate itself in the clockwise and counterclockwise inverse directions, the movable wedge 112 reciprocates along the length of the molds.
The movable wedge 112 and the stationary wedge 111 of the wedging unit 110 are stacked vertically in contact with each other. As shown in FIG. 13, contacting surface 113 of the movable wedge 112 is in contact with the stationary wedge 111, and is formed of a plurality of inclined planes 113a.about.113g having angles of inclination .theta.1.about..theta.7, and the contacting surface 114 of the stationary wedge is also formed of inclined planes 114a.about.114g having angles of inclination .theta.1.about..theta.7 respectively. The inclined planes 114a.about.114g of the stationary wedge 111 are respectively the same as the inclined planes 113a.about.113g of the movable wedge 112, wherein each pair of planes contacting each other have identical angles of inclination .theta.1.about..theta.7 are disposed in vertical engagement with their slopes being vertically inverse.
Among those inclined planes 113a.about.13g of the movable wedge 112 and the planes 114a.about.114g of the stationary wedge 111, the planes 113d and the planes 114d at the center positions are respectively set via the largest angle of inclination .theta.4, followed by the planes 113c, 114c, 113e, and 114e on both sides of the planes 113d and 114d which have the next largest angles of inclination .theta.3 and .theta.5. The angles of inclination decrease towards both ends. Angles of inclination .theta.1.about..theta.4 of the planes 113a.about.113d and 114a.about.114d from the left ends to the center are respectively related according to the expression .theta.4&gt;.theta.3&gt;.theta.2&gt;.theta.1, whereas angles of inclination .theta.5.about..theta.7 of the planes 113e.about.113g and 114e.about.14g at the right one-half are respectively related according to the expression .theta.5&gt;.theta.6&gt;.theta.7, where .theta.5=.theta.3, .theta.6=.theta.2, and .theta.7=.theta.1. In FIG. 13, and FIGS. 3, 7, 9 and 11 described later, the angles of inclination of respective planes are magnified in order to facilitate explanation, however, actual angles of inclination do not permit visual confirmation.
Simultaneous with descending movement of the ram 104 caused by driving of a pair of linear driving units 107L and 107R disposed on both sides of the ram 104, a workpiece is pressed into a V-shaped groove on the lower mold 102 by the upper mold 101 and thus bent by a certain angle corresponding to the pressing amount. Because of the pressure applied by the bending, a curved deflection shown via broken line in FIG. 14, is generated along the length of the ram 104 and the bed 106. When operating such a press brake equipped with a pair of driving units 107L and 107R set on both sides thereof, deflection of the ram 104 and the bed 106 increases toward the center portions. In FIGS. 14,15 and 16, curved deflection of the ram 104 and the bed 106 is shown to be magnified, however, actual deflection does not permit visual confirmation.
Assume that the amounts of the deflection of the ram 104 and the bed 106 in the bending process are respectively measured at the center positions X1.about.X7 in portions A.about.G corresponding to the above-referred inclined planes 113a.about.113g and 114a.about.114g, and the amounts of deflection are "10" at X4 of the center portion D, "9" at X3 and X5 of the portion C, E, "7" at X2 and X6 of the portion B, F, and "4" at X1 and X7 of the both end portions A, G, then, respective sums of deflected amounts of the ram 104 and the bed 106 at the positions X1 through X7 are "20" at X4, "18" at X3 and X5, "14" at X2 and X6, and "8" at X1 and X7, respectively.
It is assumed that such a state in which the upward planes 113a.about.113g of the movable wedge 112 and the downward planes 114a.about.114g of the stationary wedge 111 are respectively in firm contact with each other without slipping is introduced as the reference condition in which no amount of adjustment is required. When the reciprocating unit 120 is driven to cause the movable wedge 112 to be shifted to the left (shown via arrowed line in FIG. 13) from the reference condition, the stationary wedge 111 is pushed upward as per the wedge principle, and the stationary wedge 111 is upwardly displaced by an amount of displacement corresponding to the shifted amount of the movable wedge 112.
The upward planes 113a.about.113g of the movable wedge 112 are respectively in contact with the corresponding downward planes 114a.about.114g of the stationary wedge 111, although the center planes 113d and 114d of the movable wedge 112 and the stationary wedge 111 respectively have the largest angle of inclination ".theta.4". Therefore, assume that a pressure is applied to the stationary wedge 111 when it is displaced upward by the shift of the movable wedge 112, an amount of displacement at the center portion D is the largest, whereas the degree of upward displacement is gradually descended toward the end portions A and G to cause the stationary wedge 111 to curve the whole length.
When the respective angles of inclination .theta.1.about..theta.7 are set so that the ratio of the sums of deflected amounts of the ram 104 and the bed 106 at the respective center positions X1 through X7 of the portions A through G coincides with the ratio of respective angles of inclination .theta.1.about..theta.7 of the inclined planes 113a.about.113g, and 114a.about.114g and the movable wedge 112 is shifted by a predetermined distance to cause the stationary wedge 111 to displace to such an extent that the sum of deflected amounts at the center position X4 of the portion D is "20", the amounts of displacement of the stationary wedge 111 become "18" at X3 and X5, "14" at X2 and X6, and "8" at X1 and X7, thus the curved deflection of the ram 104 and the bed 106 is properly corrected. In consequence, the distance between the upper mold 101 and the lower mold 102 is kept constant along the length of the workpiece, thus making it possible to bend the workpiece at a proper bending angle.
However, it should be understood that range a of pressure applied to a workpiece subject to a bending process via a press brake is not always be constant due to lengthwise differences per kind of the workpiece Length L of a workpiece W shown in FIG. 15 is shorter than distance "d" between the pair of driving units 107L and 107R disposed on both sides, whereas length L of another workpiece W shown in FIG. 16 substantially corresponds to the whole length D of the press brake unit.
The above press brake is of such a structure that the ram 104 is subject to pressure at the positions of the driving units 107L ad 107R, whereas the bed 106 is loaded at the positions of a pair of frames 108L and 108R respectively aligned with the driving units 107L and 107R. Therefore, deflected conditions of the ram 104 and the bed 106 are different in accordance with the length L of workpieces W.
In such a case in which the length L of a workpiece W is shorter than distance "d" between the driving units 107L/107R, the ram 104 and the bed 106 during the bending process are respectively deflected into curved forms shown by P1 and Q2 in FIG. 15.
Conversely, if the length L of a workpiece W substantially corresponds to the whole length D of the press brake unit, the ram 104 and the bed 106 during the bending process are respectively deflected into curved forms shown by P2 and Q2 in FIG. 16.
In the curved deflection shown in FIG. 15, assume that the respective deflected amounts of the ram 104 and the bed 106 at the center positions X1.about.X7 of respective portions A.about.G are "10" at X4 of the center portion D, "9" at X3 and X5 of the side portions C and E, "7" at X2 and X6 of the portions B and F, and "4" at X1 and X7 of the end portions A and G, sums of deflected amounts of the ram 104 and the bed 106 at positions X1.about.X7 are "20" at X4, "18" at X3 and X5, "14" at X2 and X6, and "8" at X1 and X7. Whereas in the curved-form deflection shown in FIG. 16, assume that the respective deflected amounts are "10" at X4, "7" at X3 and X5, "2" at X2 and X6, and "3" at X1 and X7, sums of deflected amounts are "20" at X4, "14" at X3 and X5, "4" at X2 and X6, and "6" at X1 and X7.
According to the curved deflection shown in FIG. 15 and the other curved deflection shown in FIG. 16, ratios of the deflected amounts at positions X1.about.X7 are not identical to each other. In consequence, when operating the above-cited conventional adjusting unit 100, the curved deflection shown in FIG. 15 can properly be compensated, but the curved deflection shown in FIG. 16 cannot be compensated, so it is impossible to deal with workpieces having a variety of length, thus raising a problem.